1. Field of the Invention
This invention relates to a structure for rotatably supporting a rotary member, particularly, of a thin axial thickness such as pulley or gear, which may hereinafter be called "rotatably supporting structure".
2. Description of the Prior Art
In order to support a rotary member such as pulley or gear, it is generally practiced, as shown in FIG. 5 which is an axial cross-section of a typical prior art structure for supporting such a rotary member thereon, to fix one end of a shaft 1 on a fixed member 2 and after fitting the a central bore 4 of a rotary member 3 (a member to be supported rotatably) on the shaft 1, to fit a stopper ring 6 in a ring slot 5 formed in the free end of the shaft 1 so as to prevent the rotary member 3 from slipping off from the shaft 1.
In the case of the rotatably supporting structure depicted as prior art in FIG. 5, two assembly steps are required so that after fitting the rotary member 3 on the shaft 1, the stopper ring 6 is fitted in the ring slot 5. This rotatably supporting structure is however accompanied by a drawback that it cannot be efficiently assembled, especially, because the fitting work of the stopper ring 6 is cumbersome.
Further, it is not advantageous from the viewpoint of cost reduction to use small parts like the stopper ring 6. It has hence been desired to avoid use of such small parts.
In order to fit the stopper ring 6, the free end of the shaft 1 extends out significantly from the rotary member 3 by a length l. This has resulted in an inconvenience that the length of the shaft 1 cannot be shortened to any significant extent even if the rotary member 3 is made thinner.
In order to avoid the outward extension of the shaft 1 from the rotary member 3, it is also practiced, as shown in FIG. 6, to enlarge the central bore 4 of the rotary member 3 from its axially intermediate portion to its end face so as to form a large-diametered recess 7 and then to secure the rotary member 3 on the shaft 1 via a washer 8 within the large-diametered recess 7. This design however leads to a reduction to the supporting length L of the shaft 1 for the rotary member 3 by a length equivalent to the depth of the large-diametered recess 7, so that the axis of the shaft 1 and that of the rotary member 3 may not be coincided, in other words, the rotary member 3 may not be rotated smoothly.